Sound-reproducing mechanism



April 28, 1931. p. ROBBINS 1,803,038

SOUND REPRODUCING MECHANISM Filed May 17, 1929 ill ll l l lh lhl lhlllullln Patented Apr. 28, 1931 UNITED STATES PATENT OFFICE PERCY A. ROBBINS, OF HIGELAN D PARK, ILLINOIS SOUND-REPB-ODUCING MECHANISM Application filed May 17, 1929. semi no. seaosr a strip of suitable material a sound trace of substantially constant width but having an undulatory form in the lane of the strip. This sound trace is pre erably formed of paralim netic material but may also be a band 0% diamagnetic qualities formed by similar spaced undulations on the adjacent sides of two bands of paramagnetic material. This strip is caused to travel close to the poles of an electro-magnet. Interposed between one pole of this magnet and the strip is a wire coil in which an electric current is induced by the lateral shifting of the sound trace, which causes the magnetic flux to shift and cut the conductor of the coil to generate a current therein which maybe suitably amplified and converted into sound waves. The invention is hereinafter more specifically described and is illustrated in the acao companying drawings in which Fig. 1 is. a plan view of apparatus constructed in accordance with my invention;

Fig. 2 an'end elevation partly in section;

Fig. 3 a plan view of a modified form; and.

Fig. 4 a side elevation of Fig. 1.

l is the sound record, which will usually be formed as a strip of material such'as the celluloid film of kinematographic apparatus 49 and which, when the invention is used in connection with such apparatus, will bear the usual series of pictures thereon. On this strip is formed a sound trace 2 by the application of a coating of paramagnetic material to the surface of the film. This coating will usually be formed of substantially even thickness throughout its length and of substantially constant width.

In Fig. 1 the sound trace is formed of an 50 undulatory band of the paramagnetic material applied to the face of the strip. In Fig. 3 I show thesound trace as formed by removing a narrow band of the aramagnetic material between the edges 0? a wider band having its edges substantially parallel to the sides of the strip. In this case, as in the construction shown in Fig. 1, the total width of the aramagnetic material isconstant at all points in the length of the strip.

This sound record is used with apparatus of which two forms are shown. Referring particularly to Figs. 1 and 2, 3 is an electro- Vmagnet between thepole pieces of which the strip 1 passes. The pole adjacent the surface of the strip on which the sound trace is formed is preferably triangular in section as shown to concentrate the magnetic field as much as possible. Surrounding this pole piece is a coil 4, the axis of which extends transversely of the moving strip.

From this it follows that a concentration of the lines of force of the magnetic field occurs where the sound trace passes through the magnetic field adjacent the pole piece within the coil 4 and, as this point of concentration is constantly shifting lengthwise of the coil, the conductor of the coil is cut by the moving magnetic concentration in such a manner as to generate a current therein which may be suitably amplified and converted into sound waves.

In Fig. 3 I show a modification of the construction in which the pole pieces of the electro-magnet 3 are positioned on the same side of the strip 1 of the sound record and in which the helical coil 4 has a flat coil 5. substituted therefor. The mode of operation is, however, substantially the same.

While it is preferable that the sound trace should be formed by the application of paramagnetic material to the strip 1, the strip might be formed of any material having di erent magnetic qualities from the material with which the strip is formed and such will fall within the scope of my invention.

What I claim is:

1. Sound reproducing apparatus comprising a sound record comprising a strip having a sound trace formed thereon of constant width but having an undulatory form in the lane of the strip, said trace being formed y paramagnetic material applied to the strip having a substantially constant total width and of the same thickness at all points in the length of the trace; a magnet positioned to create a magnetic field ad'acent the sound trace; a coil interposed etween a magnet pole and the sound trace so that the turns of its conductor are out at varying points by the dense magnetic flux concentrated through the paramagnetic material of the sound trace as said flux shifts due to the undulations of the sound trace when the said strip is moved through the magnetic field.

2. Sound reproducing apparatus com rising a sound record comprising a strip aving a sound trace formed thereon of constant width but having an undulatory form in the plane'of the strip, said trace being formed by paramagnetic material applied to the strip having a substantially constant total width and of the same thickness at all points in the length of the trace; a magnet positioned to create a magnetic field adjacent the sound trace; and a flat coil interposed between a magnet ole and the sound trace so that the turns of its conductor are cut at varying points by the dense magnetic flux flowing through the paramagnetic material of the sound trace as said flux shifts its position relative to the coil due to the undulations of the sound trace when the 7 said strip is moved. through the magnetic 3. Sound reproducing apparatus comprising a sound record comprising a strip having a sound trace formed thereon of constant width but having an undulatory form in the plane of the strip, said trace being i formed of material having a magnetic permeability dilferent from that of the material at each side thereof; a magnet positioned to create a magnetic field adjacent the sound trace; a coil partly interposed between a magnet pole and the sound trace so that certain of the turns of its conductor are cut at varying points by the lateral shift of the certain concentrated lines of force in the magnetic field due to the undulations of the sound trace when the said strip is moved through the magnetic field.

Signed at Highland Park, 111., this 8th day of May, 1929.

PERCY A. ROBBINS. 

